This invention is related to the foaming and crosslinking of unsaturated polyester resins at elevated temperatures using as a gas generating system a t-alkyl hydrazinium salt or a carbonyl hydrazine in combination with a free radical source.
The foaming and crosslinking (or curing) of unsaturated polyester resins are well known in the prior art. U.S. Pat. No. 4,393,148 discloses the foaming and curing of an unsaturated polyester resin at ambient temperatures using a peroxide curing agent, an iron or copper metal salt promoter, and a t-alkyl hydrazinium salt as a blowing agent. U.S. Pat. No. 4,435,525 discloses the foaming and curing of an unsaturated polyester resin at ambient temperatures using a peroxide curing agent, an iron or copper metal salt promoter, and a carbonyl hydrazine as a blowing agent. Neither of these references discloses the present invention. Published European patent application no. 0048050 discloses the foaming and curing of an unsaturated polyester resin using a peroxide curing agent, an organometallic salt promoter, and a t-alkyl hydrazine blowing agent.